The present invention relates to a charge type deflecting device for a charging binary type multi-nozzle ink jet printer.
In an ink jet printer of the general type to which the invention pertains, ink particles not used for printing are charged so that they can be deflected perpendicularly to the primary direction of the ink jet by application of a deflecting field formed by deflecting electrodes. The deflected particles are recovered in a gutter. As the ink particles used for printing are not charged, they pass straight through the deflecting field to strike against the recording medium to print a desired image as a pattern of dots.
FIG. 1 is a schematic diagram showing the essential components of a conventional ink jet printer including therein nozzles 3, a charging electrode plate 4, ink jet passing holes 4A formed in the plate 4, a charging electrode 5 formed on the inner wall of each hole 4A, an upper deflecting electrode 6, a lower deflecting electrode 7, a gutter 8, a recording medium 9, a deflecting electrode DC source 11, and a printing signal generator 12.
In the conventional ink jet printer, the charging electrode plate 4 is prepared by forming a plurality of ink jet passing holes 4A in a single insulating plate made of a ceramic material or the like and by coating the inner walls of the holes 4A with electrically conductive material. The nozzles 3 are formed as a plurality of minute holes arranged linearly in an orifice panel. The ink jet from each nozzle 3 is separated at a certain position into ink particles or droplets. However, it should be noted that the ink jet separating position is different for different nozzles 3.
The distance between the end of the nozzle and the ink jet separating position, termed the "separating length", depends on various conditions although the distance is usually 0.5 mm to 2 or 3 mm. In a practical ink jet printer, the variation in the ink jet separating positions is selected so that it is less than one-half to one-fourth of the distance between adjacent droplets in the ink jet from one nozzle 3.
Ink particles not used for printing are charged by a charging electrode plate provided at the ink jet separating position. Voltages are applied to the electrodes 5 of the electrode plate according to printing signals provided by the printing signal generator 12.
As described above, in the conventional ink jet printer, all of the charging electrodes 5 are provided in a single charging electrode plate 4. Therefore, if an ink jet is separated into ink particles at a position which is shifted from the charging electrode position, for some reason such as a nozzle being dirty, then the particles are not charged irrespective of the presence or absence of the printing signal. Accordingly, all the ink particles then move straight towards the recording medium 9 resulting in the recording of noise.
This difficulty may be alleviated somewhat by increasing the thickness of the charging electrode plate 4. However, the diameter of each charging electrode 5 is very small, about 0.3 mm. Therefore, as the thickness of the electrode plate 4 is increased, it becomes difficult to align the ink jets with the charging electrodes so each of the ink jets is directed through the corresponding charging electrode 5.
Accordingly, an object of the invention is to provide an ink jet printer in which the particles which are separated from an ink jet at a position shifted from the charging electrode position are charged at all times thereby to prevent the separated ink particles from reaching the recording medium.